1. Field of the Art
This invention relates to a catheter type ultrasound probe with an ultrasound transducer at the distal end of a catheter member for intracorporeal inspections or examinations, and more particularly to a catheter type ultrasound probe which is equipped with a puncture needle with improved penetration characteristics.
2. Prior Art
Ultrasound examination systems are generally arranged to transmit ultrasound pulses into an intracorporeal portion of interest from an ultrasound transducer element while receiving and processing return echo signals to produce video signals of tomographic ultrasound images for display on a monitor screen. The known ultrasound examination systems include the so-called catheter type ultrasound probe having an ultrasound transducer element mounted at the distal end of a narrow catheter member to be inserted into an intracorporeal portion to be examined. In case a diseased portion is spotted by an ultrasound examination, it is the general practice to use a puncture needle for various purposes, for example, for injecting a medicine into the diseased portion, for injecting contrast media for closer examination, for sampling tissues from the diseased portion, or for drainage. The puncture needle of this sort usually has a hollow body which is sharp-pointed at its fore end to penetrate a targeted intracorporeal portion to a predetermined depth. In such a puncturing operation, a puncture needle is directed toward a diseased portion or other target portion which needs a treatment, confirming the needle position by way of an ultrasound image which is displayed on a monitor screen.
Naturally, some catheter type ultrasound probes are constructed to permit the use of a puncture needle of the sort as mentioned above, the puncture needle being launched through a needle guide passage which is provided on a catheter member of the ultrasound probe. In this regard, the operation of needle penetration into a diseased portion is likewise monitored through ultrasound images displayed on a monitor screen of an ultrasound image observation terminal of the examination system. Therefore, the puncture needle should always be within the view field of the ultrasound image under observation. The view filed in the ultrasound image observation is produced by an ultrasound scanning operation, for example, by a B-mode scanning operation in a linear or convex scanning mode under either mechanical or electronic drive. For instance, for an electronic linear or convex scanning operation, a large number of transducer elements which constitute the ultrasound transducer are arrayed in a row on lateral side portions of a tip end portion of the catheter member of the probe to take a view field in a direction perpendicular to the axis of the catheter member. A puncture needle therefore needs to be launched into the view field of the ultrasound image under observation from a position on the near side of the ultrasound transducer. For this purpose, the needle guide passage which guides the puncture needle along the axis of the catheter member is turned through an obliquely curved passage toward an exit which is opened on a lateral side portion of the catheter member at a position on the near side of the ultrasound transducer.
In this connection, from the standpoint of protection of patients and higher target hitting characteristics, the puncture needle point Should preferably be driven out of the needle passage in such a way as to penetrate a target or diseased portion from as close a position as possible through an intracavitary wall, and from a needle guide passage which is as short as possible in length. To this end, attempts have been made to project a needle point from an exit which is opened at a position close to the ultrasound transducer. For instance, in case of driving a puncture needle into the pancreas through a stomach wall from a needle passage on a catheter member which has been inserted into the stomach, it has been considered that the optimum needle launching angle relative to the axis of the catheter member is 30.degree.. This means that the axial needle passage has to be arranged to turn its direction by approximately 30.degree. toward its exit through a curved needle passage to comply with the optimum needle launching angle.
Further, considering the thrust which is required to drive a puncture needle for penetration into a diseased portion through an intracavitary wall, the puncture needle is preferred to be formed of a hard rigid material at least in its projectile portion to be launched from the needle passage. However, with a needle body of high rigidity, it is difficult to switch the needle direction at an angle as large as 30.degree.. In this regard, the conventional procedure has been to resort to a flexible needle which can easily bend itself through such an angle for a turn toward the exit opening of the needle passage, sacrificing to some extent the thrust for the needle penetration through intracavitary walls.